Because polyolefin, such as polyethylene (PE), polypropylene (PP), etc., is lightweight and inexpensive and has superior properties and processability, it is widely utilized in a variety of fields including food packaging, medical/cosmetic/pharmaceutical containers, car parts, communication/electric device parts, building/construction materials, agricultural materials, medical devices, etc. and thus occupies a very important position as a general-purpose resin. However, needs for properties of polyolefin are still more diversified these days. For example, there are demands for polyolefin having properties which do not exist in conventional polyolefin, including polyolefin having high heat resistance or polyolefin having a flexible texture such as soft polyvinyl chloride, and also polyolefin imparted with high functionality such as printability, coatability, adhesion and compatibility with a polymer having different polarity.
An ethylene-based copolymer is originally non-polar because it has no polar group in the molecule thereof, and thus has poor attachment strength to a highly polar material such as a metal or polar resin.
For this reason, when an ethylene-based copolymer is bound with a highly polar material, the surface of the ethylene-based copolymer has to be treated using firing treatment, corona discharge treatment, primer treatment, etc., and thus complicated preparation problems may occur.
A metallocene compound indicates a Group 4 transition metal compound having one or two cyclopentadienyl groups as a ligand, and may be activated using methyl aluminoxane or a boron compound and may thus be used as a catalyst for olefin polymerization. Because such a metallocene catalyst has a uniform active site, the molecular weight distribution of a polymer is narrow, copolymerization becomes easy, and the distribution of a second monomer is uniform. In the case of propylene polymerization, the stereostructure of the polymer may be advantageously adjusted depending on the symmetry of the catalyst. In particular, although only isotactic polypropylene may be prepared using a conventional Ziegler-Natta catalyst, the use of the metallocene catalyst enables preparation of polypropylene having different tacticities such as isotatic, syndiotactic, atactic, hemiisotactic, etc. For example, syndiotactic polypropylene synthesized using metallocene is characterized in terms of low crystallinity, appropriate rigidity and hardness, high transparency and superior impact resistance.
The metallocene catalyst is actively utilized to produce copolymers of ethylene and α-olefin, such as LLDPE, VLDPE, EPM and EPDM, cycloolefin copolymers (COC) of ethylene and cycloolefin or α-olefin and cycloolefin, and copolymers of ethylene and α-olefin and styrene. The catalytic conditions required commonly for preparation of such products should have high activity and high reactivity for the second monomer, and should enable the preparation of a polymer having a uniform second monomer distribution.
Meanwhile, because the metallocene catalyst is more expensive compared to a conventional Ziegler-Natta catalyst, it is regarded as being economically valuable when having high activity. Especially in the case of a catalyst having good reactivity for the second monomer, a polymer having the second monomer in a large amount may be favorably obtained even when the second monomer is used in a small amount.
Anionic polymerization is comparatively complicated in terms of purification of monomer and solvent or because of the requirements for low temperature and high vacuum upon initiator handling and polymerization, but may very precisely control the molecular weight or molecular weight distribution of a polymer (M. Morton et al., Rubber Chem. Technol, 1975, 48, 359; M. Morton, “Anionic Polymerization, Principles and Practice”, 1983, Academic Press, Inc., NY; M. Szwarc, “Carbanions, Living Polymers and Electron Transfer Process”, 1968, Wiley (INterscience), NY). Since a living mechanism has been found in the polymerization for some kinds of monomers by Szwarc, systematic study for anionic living polymerization has been carried out and various kinds of monomers have been polymerized using anionic polymerization. In domestic cases, thorough research into various kinds of polymer blends is ongoing. In this research, there is a need for much of the same material, such as a block copolymer or a polymer standard material having low molecular weight distribution or accurately controlled molecular weight, but there is extremely lack of study thereto. The styrene-based standard material or the styrene-diene-based block copolymer may be supplied from abroad but is very limited in terms of molecular weight or block size, and samples for polar polymers cannot be ensured at all. Although synthesis of some block copolymers using anionic polymerization has been performed in recent years, synthesis is mostly carried out using a break seal method, and thus the amount of the prepared sample approximates to 10 g. Accordingly, research into mass synthesis by anionic polymerization is required. Culminating in the present invention, intensive and thorough research carried out by the present inventors aiming to solve the problems encountered in the related art, resulted in the finding that an ethylene monomer, an α-olefin monomer having 6 to 12 carbon atoms, and at least one functional monomer selected from the group consisting of divinylbenzene and p-methylstyrene may be polymerized at a predetermined molar ratio using a metallocene catalyst to thus prepare a main chain, and then a polar polymer for imparting functionality may be subjected to anionic polymerization and thus introduced as a side chain, thereby synthesizing a highly elastic ethylene-based pluralistic copolymer composed of a highly elastic main chain and a graft side chain for imparting functionality, with superior mechanical strength, such as scratch resistance, hardness, elongation and fracture strength.